Semiconductor devices such as diodes and the like are used widely in power conversion circuits, etc. When switching a power supply from the ON state to the OFF state in a power conversion circuit, a surge voltage is applied to the diode due to the parasitic inductance component inside the circuit connected to the diode. At this time, there are cases where the electric field inside the diode exceeds the critical electric field due to the surge voltage; impact ionization occurs; and avalanche breakdown occurs.